We report on the field assessment of the Mars (TM) optical soiling sensor performance for PV-soiling measurement under harsh conditions of a desert environment. Mars (TM) was installed in a hot, sunny, and dusty climate in the Outdoor Test Facility, managed by Qatar Environment & Energy Research Institute, located in Doha (state of Qatar). Mars (TM) is a compact system, easy to install at different geographical sites, and it is designed to allow an efficient and cost-effective PV-soiling measurement with lower labor and operation & maintenance requirements, compared to conventional soiling measurement requiring conventional clean/soiled reference module pair method. Despite some discrepancy in the soiling measurements that were more pronounced during certain periods of time than the others, overall, a good fit was noticed between the two methods. A mismatch of less than similar to 0.1 %/day between the light transmission loss estimated by the Mars (TM) sensor and from a PV array is identified, and results are discussed accordingly. We demonstrate thus the feasibility of Mars (TM) to be deployed in different geographical locations and it's potential in measuring wide range of PV-soiling in commercial-scale PV installations.